Forensic Science Journal FORENSIC SCIENCE 2008;7(1):37-44 JOURNAL SINCE 2002 Available online at:fsjournal.cpu.edu.tw

Particle analysis of lighter flint residues using scanning electron microscopy/energy dispersive X-ray spectrometry

Hsien-Hui Meng,1,* Ph. D.; Chun-Hung Lin,2 B. Sc.

1 Department of Forensic Science, Central Police University, Taoyuan, 33304, Taiwan, ROC. 2 Forensic Science Section, Pintung Police Headquarters, Taiwan, ROC.

Received: October 24, 2008 / Accepted: November 20, 2008

Abstract The sparking flints used in lighters were reported to generate particles that look like gunshot residue particles. They are spheres and consist of iron and some rare earth metals. Eleven lighters purchased from local stores were used to produce flint residues in this work. The residue samples and flint rods and metal wheels removed from lighters were analyzed using scanning electron microscopy/energy dispersive X-ray spectrometry. The results reveal that most of the lighter flint residue particles containing rare earth metals are spheroidal. The elemental composition detected in flint residues can be classified into three classes: Al-Fe-Ce-La, Fe-Ce-La, and Fe-Ce. Six lighters produced flint residues containing Fe-Ce-La; four lighters gave residues of Al-Fe-Ce-La; one lighter produced flint residues of Fe-Ce. The results also indicate that the elemental composition of lighter flint residue is highly correlative with the composition and construction of the flint rod. The lighters’ flint rods are made of ferrocerium containing iron and rare earth metals which are scarcely encountered in daily life. The detection of spheroidal particles containing iron and rare earth metals provides a way to identify lighter flint residues. These characteristic residues can be used as trace evidence in crime cases where the linkage between a lighter user and another persons or places is to be established. Furthermore, since the elemental profile of lighter flint residues is totally different from that of GSR, the lighter flint residues would not affect the identification of gunshot residues at all.

Keywords: forensic sciences, trace evidence, particle analysis, lighter flint residues, gunshot residues, scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS)

Introduction to identify all elements heavier than sodium contained in Inorganic gunshot residues (GSR) consist of GSR particles. Elemental composition of lead, antimony, discrete, micrometer-sized particles, predominantly and barium has been observed only in gunshot residues spheroidal, and often of characteristic appearance. and are therefore considered characteristic of GSR These GSR particles can arise from the primer mixtures, [3]. The spheroidal morphology of the particles allows the bullet, the cartridge case, the propellant powder, them to be discriminated from the general debris lifted and GSR deposited inside the barrel from previous from the hand and other surfaces under the secondary discharge of cartridges while discharging a firearm electron imaging mode, and the higher atomic numbers [1,2]. The unique elemental profile and characteristic of their characteristic elements allow them to be found spherical shape of GSR are usually identified using as brighter particles among the darker background under scanning electron microscopy/energy dispersive X-ray the backscattered electron imaging mode. spectrometry (SEM/EDS) which allows the identification An article published in New Scientist magazine of a single GSR particle in non-destructive way and in 2005 argued about the probative value of forensic gives a high selectivity unparalleled by any bulk analysis examination of gunshot residues. The article raised a methods. The energy dispersive X-ray analyzer is able number of critical issues including the uniqueness of

* Corresponding author, e-mail: [email protected] 38 Forensic Science Journal 2008; Vol. 7, No. 1

GSR particles, criteria for the identification of GSR, Locard’s Exchange Principle whenever a person comes contamination of GSR via secondary transfer and into contact with an object or another person a cross- environmental and occupational particles [4]. A number transfer of physical evidence occurs. By searching, of environmental and occupational particles that might recognizing, collecting, and examining the transferred interfere the identification of GSR have been examined evidence criminals could be linked with crime scenes [5, 6, 7, 8, 9, 10, 11]. These interfering particles might and victims [12]. This brings out a possibility that lighter originate from stud guns, cap guns, pyrotechnics, brake flint residue can be used as a trace evidence to confirm linings, lead smelting, lead-acid battery, and lighter possible contacts between a lighter user and another flints. In late 1970s, research results indicated that none persons or objects. This work focused on the SEM/ of these environmental and occupational samples was EDS analysis of lighter flint residues collected from the falsely identified as gunshot residue by the experienced surface of used lighter and hand of the user. Hopefully, analysts; however, less experienced personnel may the results of this work would provide a practical way to sometimes have encountered difficulties [6]. However, identify the lighter flint residue evidence on crime cases later literatures revealed that elemental profiles of brake where a lighter user is involved. linings and pyrotechnics are similar to that of GSR. A feasible technique employed to distinguish these particles from GSR particles is X-ray mapping [7, 8, 9]. Elemental profile is the most definitive characteristic of a Experimental GSR particle, thus micrometer-sized spheroidal particles of various origins other than GSR are usually easily Instruments and materials excluded as being composed of elements other than lead, 1. JSM-5410LV Scanning Electron Microscope barium, and antimony and do not constitute a problem (SEM), Jeol, Japan. Acceleration voltage: 20 KV. [3]. Lighter flint residue is one kind of these non-Pb- Tilt of sample: 0˚. Working distance: 15 mm. Ba-Sb micrometer-sized spheroidal particles which Images observed: secondary electron images and has been regarded as being with a clearly identifiable backscattered electron images. separate origin [5]. The sparking flints used in cigarette 2. LINK ISIS energy dispersive X-ray analyzer (EDX), lighters were reported to generate particles that look like Oxford, UK. X-ray signals were collected from 0 GSR particles under the SEM observation during the to 20 KeV, 20 eV per channel. Peaks were either ignitions of the lighters. They were described as being manually or automatically identified. spheres, sometimes porous like a sponge, and consist of 3. Ten disposable lighters and one military-typed lighter iron and some rare earth elements [6]. The same article were used in this work. One disposable lighter and also revealed that lighter flint residues were occasionally the military-typed lighter are shown as Figs. 1 and found on the hand of a nonsmoker. According to 2. Details of lighters employed for test ignitions and samples analyzed are shown in Table 1.

Table 1 Details of lighter and samples analyzed. Sample name Brand a Type of lighter Samples analyzed D1 弼臣 Disposable Flint residues D2 弼臣 Disposable Flint residues D3 千輝 Disposable Flint residues D4 千輝 Disposable Flint residues & flint rod D5 萬達 Disposable Flint residues D6 鴻興 Disposable Flint residues D7 永輝 Disposable Flint residues& flint rod D8 勇士 Disposable Flint residues D9 千輝 Disposable Flint residues D10 旭輝i Disposable Flint residues M1 Zippo Military Flint residues Particle analysis of lighter flint residues using scanning electron microscopy/energy dispersive X-ray spectrometry 39

were performed and these blank samples were subsequently subjected to carbon coating and SEM/ EDS analysis. 2. Analysis of flint rods: After the analyses of flint residue samples were completed, flint rod and metal wheel from D4 and D7 disposable lighters were removed from the lighters. Each of these parts was mounted on one SEM sample stub using double- sided carbon tape. Mounted samples were coated with carbon and subjected to SEM/EDS analysis.

Results and discussion

Analysis of flint residues There were no spheroidal particles observed in Fig.1 A typical disposable lighter used in this work. all blank samples. Most of the particles in a sample of lighter flint residues that contained rare earth metals had spheroidal morphology. The samples collected around the flame ports of ignited lighters were most abundant of spheroidal particles with a wide range of sizes (Fig. 3). For samples collected from user’s hand, more spheroidal particles were detected on thumb samples than web samples. This indicates that direct contact between thumb and metal wheel transfers more flint residues toward user’s hand than flint residues carried by sparking toward the hand. For all three samples originated from the test ignitions of D4 lighter, there were only several spheroidal particles containing rare earth metals detected in each sample. This lighter was thus disassembled and the flint Fig.2 The military-typed lighter used in this work. rod and the metal wheel were removed for further SEM/ EDS analysis to find out the reason of relatively small amount of spheroidal residue particles produced during test ignitions. The results are described later in this work. Methods Spheroidal particles observed may be perfect 1. Analysis of flint residues: The metal wheel of each spheres, or their morphology may be slightly deviated lighter was rolled to strike against the flint rod to from perfect sphere, but "three-dimensional roundedness" ignite the brand new lighter for five times. Lighter is a required feature of this classification. The surfaces flint residues were then collected from the thumb and of the spheroids may be smooth, rough, or attached the web of the user’s igniting hand and the surface with smaller spheres. Occasionally, they are hollow around the flame port of the lighter using SEM or perforated spheres. Examples of different shaped sample stubs attached with double-sided carbon tape. spheroidal flint residue particles are shown as Figs. Lighter flint residue samples were then coated with 4-8. The diameters of the spheroidal particles detected carbon prior to SEM/EDS analysis. Blank samples were usually less than 30μm. Because of the limitation for each lighter tested were also collected from the of the resolution of SEM used, particles less than user’s previously cleaned hand before test ignitions 0.5μm in diameter were not analyzed in this work. The 40 Forensic Science Journal 2008; Vol. 7, No. 1

morphology of spheroidal lighter flint residue particles is nearly the same as that of gunshot residue particles. Thus flint residues cannot be differentiated from GSR solely through morphological comparison. Two typical spheroidal GSR particles are shown in Figs. 9 and 10 for comparative purpose.

Fig.6 A spherical lighter flint residue attached with smaller spheres.

Fig.3 The sample collected around flame port of an ignited lighter is abundant of different sized spheroidal particles.

Fig.7 A rough surfaced spheroidal lighter flint residue particle.

Fig.4 A perfect lighter flint residue sphere.

Fig.5 Two spherical lighter flint residue particles Fig.8 A broken hollow lighter flint residue sphere. connected to each other. Particle analysis of lighter flint residues using scanning electron microscopy/energy dispersive X-ray spectrometry 41

Fe-Ce-La. Aluminum is not a required component for either flint rod or metal wheel. The D7 lighter was thus disassembled and the flint rod and the metal wheel were removed for further SEM/EDS analysis to find out the source of Al in the residues. The D8 lighter is the only one that produced the flint residues having the simplest elemental profile of Fe-Ce. Flint rod of a lighter is made of ferrocerium that is a man-made metallic material and is able to give off a quantity of hot sparks when struck against the metal wheel. When small shavings of the flint rod are removed quickly enough, the heat generated by friction Fig.9 A rough surfaced spherical GSR particle. is enough to ignite those shavings. The sparks generated are actually micro droplets of liquidized burning metal that condensed into solid spheres after cooling down. These spherical particles would deposit on the surface of the lighter and the user’s hand, or any objects close to the igniting lighter. Modern ferrocerium product is usually composed mostly of iron, combined with an alloy of rare earth metals such as cerium, lanthanum, and neodymium. The origin of easy sparking of ferrocerium flint is cerium’s low temperature pyrophoricity, its ignition temperature occurring between 150 and 180℃ [13]. There are two more types of ferrocerium flint manufactured, the first contains just iron and cerium, and the second also includes lanthanum to produce brighter sparks. Since the flint residues are formed in a very short period of time, the reduction-oxidation reaction of the burning of the flint rod shavings has never reached Fig.10 A smooth surfaced spherical GSR particle. its equilibrium; the elemental composition of residue particles may be different from each other even they are produced from the same lighter. In spite of this, the qualitative elemental profiles of residue particles detected can still be classified into six categories as followings: (1)Fe-Ce-La; (2)Ce-La; (3)Al-Fe-Ce-La; (4)Al-Ce-La; The details of elements detected for the lighter (5)Al-Fe-Ce; (6)Fe-Ce. Typical energy dispersive X-ray flint residue samples from test ignitions of various spectra of every elemental profile are shown in Figs. lighters are shown in Table 2. Major elements detected 11-16. Particles have elemental profiles of Fe-Ce-La in lighter flint residue samples collected from flame and Ce-La occurred in all flint residue samples except port, user’s thumb, and user’s web after test ignitions of that from lighter D8. Since elements Ce and La are each lighter are in perfect accordance with each other. scarcely encountered in daily life, this elemental profile The elemental composition detected in flint residues can be regarded as the most characteristic elemental from the eleven lighters studied can be classified into composition of lighter flint residue. Particles contained three classes: aluminum-iron-cerium-lanthanum (Al- Al occurred only in samples collected from test ignitions Fe-Ce-La), Fe-Ce-La, and Fe-Ce. Six out of eleven of lighters D6, D7, D10, and M1. For samples originated lighters produced flint residues that contained Fe-Ce-La. from lighter D8, only Fe-Ce particles were detected. Four out of eleven lighters gave residues containing Al- 42 Forensic Science Journal 2008; Vol. 7, No. 1

Table 2 Elements detected in flint residues collected from various lighters.

Sample name Elements detected D1 Fe, Ce, La D2 Fe, Ce, La D3 Fe, Ce, La D4 Fe, Ce, La D5 Fe, Ce, La D6 Al, Fe, Ce, La D7 Al, Fe, Ce, La D8 Fe, Ce D9 Fe, Ce, La D10 Al, Fe, Ce, La M1 Al, Fe, Ce, La

Fig.11 An EDS spectrum of lighter flint residues Fig.12 An EDS spectrum of lighter flint residues containing Fe, Ce, and La. containing Ce and La.

Fig.13 An EDS spectrum of lighter flint residues Fig.14 An EDS spectrum of lighter flint residues containing Al, Fe, Ce, and La. containing Al, Ce, and La. Particle analysis of lighter flint residues using scanning electron microscopy/energy dispersive X-ray spectrometry 43

major peak of carbon the intensity of detected peaks is so low that these peaks can barely be identified as Fe, Ce, and La. It is thus assumed that the concentration of ferrocerium metal in D4 flint rod, which is basically a carbon rod, is relatively low and close to the detection limit of EDS technique. This result explained the reason why only a small amount of characteristic flint residue particles were detected in samples collected from the test ignitions of lighter D4. The results of flint rod analysis also indicate that the elemental composition of lighter flint residue is highly correlative with the composition and construction of the flint rod. Both D4 and D7 metal wheel samples were found to contain iron and zinc (Fig. Fig.15 An EDS spectrum of lighter flint residues 18). containing Al, Ce, and Fe.

Fig.16 An EDS spectrum of lighter flint residues Fig.17 An EDS spectrum of elements detected on containing Fe and Ce. lighter flint sample D7.

Analysis of flint rods and metal wheels In addition to carbon element, the major elements detected on the cross section of flint sample D7 are Fe, Ce, and La. A typical energy dispersive X-ray spectrum of flint rod is shown in Fig. 17 where carbon peak is not labeled. The only element detected on the rim of the flint rod is aluminum. This showed that the flint rod is wrapped with a layer of aluminum and this aluminum layer is the source of the Al detected in flint residues originated from lighters D6, D7, D10, and M1. For lighter flint sample D4, with the exception of the Fig.18 Metal wheel contains iron and zinc. 44 Forensic Science Journal 2008; Vol. 7, No. 1

Conclusions 5. Wolten GM, Nesbitt RS, Calloway AR, Loper GL, Our results reveal that the elemental components and Jones PF. Particle analysis for the detection of of lighter flint residues are highly dependent upon the gunshot residue. I: scanning electron microscopy/ composition and construction of flint rods. The flint energy dispersive X-ray characterization of hand rods of modern lighters, regardless disposable ones deposits from firing. J Forensic Sci 1979; 24: 409. or military-typed ones, are composed of ferrocerium 6. Wolten GM, Nesbitt RS, Calloway AR, and Loper containing at least one rare earth metal of cerium. In GL. Particle analysis for the detection of gunshot most of the cases, flint rods contain rare earth metals residue. II: occupational and environmental particles. of cerium and lanthanum. Since Ce and La are scarcely . J Forensic Sci 1979; 24: 423. encountered in daily life and spheroidal micro particles 7. Garofano L, Capra M, Ferrari F, Bizzaro GP, Di result only from high temperature events, the detection of Tullio D, Dell’Olio M, and Ghitti A. Further studies spheroidal particles containing iron and rare earth metals on particles of environmental and occupational using SEM/EDS provides a way to confirm the presence origin. Forensic Sci International 1999; 103: 1. of lighter flint residues. These characteristic residues can 8. Torre C, Mattutino G, Vasino V, and Robino C. be used as trace evidence in any crime cases where the Brake linings: A source of non-GSR particles linkage between a lighter user and another persons or containing lead, barium, and antimony. J Forensic places is to be established. Sci 2002; 47: 494. It is obvious that, although the morphology of 9. Cardinetti B, Ciampini C, D’Onofrio C, Orlando lighter flint residue particles is almost the same as that G, Gravina L, Ferrari F, Di Tullio D, and Torresi of GSR particles, the elemental profile of lighter flint L. X-ray mapping technique: a preliminary study residues is totally different from that of GSR. It can in discriminating gunshot residue particles from be concluded that the lighter flint residues are not the aggregates of environmental occupational origin. sources of interferences toward the identification of Forensic Sci International 2004; 143: 27. gunshot residues. 10. K o s a n k e K L, D u j a y R C, a n d K o s a n k e B. Characterization of pyrotechnic reaction residue particles by SEM/EDS. J Forensic Sci 2003; 48: 531. Acknowledgements 11. K o s a n k e K L, D u j a y R C, a n d K o s a n k e B. The authors are indebted to the National Science Pyrotechnic reaction residue particle analysis, J Council, Taiwan (ROC) for financial support. The Forensic Sci 2006; 51: 296. number of grant is NSC 95-2414-H-015-005.] 12. Chisum WJ and Turvey BE. Evidence dynamics: Locard’s Exchange Principle & crime reconstruction, References J Behavioral Profiling 2000, 1(1): 531. 1. Meng H-H, Lee H-C, Chen Y-L. The analysis 13. http://en.wikipedia.org/wiki/Ferrocerium, last visit of primer mixtures and gunshot residues using on 10/October/2008. scanning electron microscopy / energy dispersive x-ray analysis. IEEE Annual International Carnahan Conference on Security Technology, Proceedings, 2003: 358. 2. Meng H-H, Lee H-C. Elemental analysis of primer mixtures and gunshot residues from handgun cartridges commonly encountered in Taiwan. Forensic Sci J, 2007; 6(1): 39. 3. Standard Guide for Gunshot Residue Analysis by Scanning Electron Microscopy/ Energy Dispersive X-ray Spectrometry. ASTM, E 1588 – 08, 2008. 4. Mejia R. Why we cannot rely on firearm forensics. 23 Nov. 2005, New Scentist.com news service.